Fruits such as apples turn brown when they are damaged in the process of harvest, shipping and transportation thereof, and mainly due to deterioration of appearances, they may reduce or lose their commercial values. Scratch may also be generated at the time of processing into drinks such as juice or foods or cooking, and in consequence, scratch as well as browning of processed fruits may reduce their commercial values.
In particular, browning is prominent in apples. For example, when grated, cut, or frozen and thawed, browning in apple proceeds at a rapid pace compared to other fruits, and the browning degree thereof is also high. Therefore, the sale in the form of lately-increasing cut fruits or the use in the confectionery industry is consequently very limited.
Accordingly, it can be said that measures against browning in apples are an extremely important challenge for using them to be eaten raw and also for using them in processed foods such as juice or in such commercial forms as cut fruits in order to maintain their commercial value or to increase additional value.
Browning accompanies an enzymatic chemical reaction, which is caused by oxidization of polyphenols contained in plants into quinones by polyphenol oxidase, which finally results in oxidative condensation to a mealanin-like black material. If it is not limited to apples, the following measures against such browning have conventionally be proposed, including addition of an appropriate antioxidant such as ascorbic acid (Japanese Patent Laid-Open No. 10-136883), addition of kojic acid (Japanese Patent Publication No. 5-30422), addition of a fish milt extract (Japanese Patent Laid-Open No. 2000-23615), and addition of an extract of algae such as Chlorococcales (Japanese Patent Laid-Open No. 2000-139434).
Immersion treatments in Flammulina velutipes extract (Patent Document 1) and Welsh onion juice with the density of 50 to 100% (Patent Document 2) have also been proposed as measures for those particularly including an apple as an object. In view of preservation, an apple freshness-keeping package has also been disclosed, in which an apple is packed with a synthetic resin film whose oxygen transmittance is 1.5 to 5 cc/24 hr·atm per 1 g of apple so that the oxygen and carbon dioxide concentrations in the bag become 3 to 12% and 8 to 15%, respectively, and the apple respiration rate is suppressed to 30 to 80% in the atmosphere (Patent Document 3).    Patent Document 1: Japanese Patent Laid-Open No. 2003-070450 “Blackening/browning inhibitor for food”    Patent Document 2: Japanese Patent Laid-Open No. 2002-335859 “Method for preventing discoloring of fruits or processed fruits, and anti-discoloring agent for the same”    Patent Document 3: Japanese Patent Laid-Open No. 2000-004781 “Freshness-keeping package for apple”